Mobile devices may be equipped with multiple communication interfaces, such as a radio transceiver for accessing one or more cellular networks (e.g. GPRS (general packet radio service), EDGE (enhanced data rates for gsm evolution), 3GPP (third generation partnership project), 3GPP2, and CDMA2000 (code division multiple access)), as well as a radio transceiver for accessing one or more wireless local area networks (WLANs), such as Institute of Electrical and Electronics Engineers (IEEE) 802.11 (Wi-Fi) and IEEE 802.16 (WiMAX) networks. Due to bandwidth, signal strength, data charge avoidance, battery life conservation, and other considerations, many mobile devices are configured to automatically connect to and route all data through any available wireless networks.
However, all WLANs are not free. Many WLANs host a web portal (also called “captive portals”) in their default gateway or server that prevents access to the Internet (or other network) until the user of the mobile device has performed authentication, typically through entering payment information or login or password credentials or agreeing to the provider's terms of service.
Captive-portal techniques often force a Hyper Text Transfer Protocol (HTTP) client on a network to see a special Web page (usually for authentication purposes) before using the Internet normally. A captive portal turns a Web browser into an authentication device. This may be done by intercepting all packets, regardless of address or port, until the user opens a browser and tries to access the Internet. At that time, the browser may be redirected to a web page that requires authentication or payment or displays an acceptable use policy that the user must agree to. Until successful authentication, the user device may be “trapped” in the portal's “walled garden.” Captive portals are often used at Wi-Fi hotspots and may be used to control wired access (e.g. in apartment houses, hotel rooms, business centers, or “open” Ethernet jacks) as well. Captive portals may use a wide variety of packet-interception techniques, such as HTTP Redirect, IP Redirect, and Domain Name Server (DNS) Redirect.